Prime Minister Theresa May was back in UK parliament for day three of a debate to sell her Brexit deal to ministers ahead of a key vote next week.
The House of Commons leader, Andrea Leadsom, told parliament the vote on December 11 would go ahead.
The announcement came amid suggestions from ministers that she should find ways to avoid losing the vote, which could bring down the government, or see Britain leave the bloc without a deal.
However, May is widely expected to lose the vote, mainly due to the issue of the Irish backstop.
Brexiteers and Northern Ireland's Democratic Unionist Party, which props up May's government, worry that the proposed deal could leave Britain under EU regulations indefinitely, or Northern Ireland could be treated differently to the rest of the UK.
The EU's chief negotiator, Michel Barnier, said the UK's future is at stake in the Brexit vote on Thursday.
"Now is now the moment for everyone to bear their responsibilities. You know the British parliament will give its verdict on this text and on the future relationship in the coming days. It is a vote in which the future of their country is at stake," he said.
Barnier reiterated previous comments that May's deal, which was agreed with the EU in November, was the best on offer.
“The agreement that is on the table — the withdrawal agreement and the agreement on the future relationship — are, in our view, the only and best possible to organise an orderly withdrawal,” he said.
The three Brexit options- according to May
The UK Prime Minister told the BBC earlier on Thursday: "There are three options: one is to leave the European Union with a deal ... the other two are that we leave without a deal or that we have no Brexit at all," May said.